This invention relates to a device for adjusting the phase of a flat screen in an automatic flat screen dye printing or automatic flat screen printing machine. More particularly, the invention relates to a device for adjusting the phase of a flat screen which can perform the phase adjustment of a flat screen independently from the screen driving system and can adjust the phase of a flat screen not only when the printing machine is stopped but also when the printing machine is in operation.
In conventional automatic printing machines, an endless belt for supporting and transporting a material to be printed, such as cloth, is fed intermittently and while the endless belt is stopped, a screen is brought down on the material to be printed, and then, a squeegee member is scanned on the screen to squeeze out a printing paste on the material to be printed and the screen and squeegee member are lifted up and the endless belt is fed again.
In this conventional printing method, problems are involved in intermittent feeding of a material to be printed. For example, in order to register the material to be printed exactly with the screen, it is necessary to use an expensive printing belt (blanket) which has a much reduced tendency to elongate and a belt-stopping mechanism having a very high accuracy, and therefore, the structure of the printing machine is inevitably complicated and its price is very high. Further, when a flexible material is printed, an accurate pattern can hardly be printed because of a tension given when it is transported.
Recently, as a printing method overcoming the foregoing disadvantages, there has been proposed an automatic screen printing method comprising feeding continuously a material to be printed at a constant speed in the longitudinal direction by means of a transporting member, bringing down a printing stencil (screen), which has been positioned above the material to be printed, on the material to be printed to contact the stencil with the material to be printed, moving both the printing stencil and the material to be printed at the same speed in the same direction, squeezing out a printing paste on the material to be printed while the printing stencil travels along a length corresponding to about 1/2 of the pattern length, lifting up the printing stencil to release its contact with the material to be printed, moving the printing stencil in the reverse direction, and repeating the foregoing operations (see the specification of U.S. Pat. No. 3,168,036).
This automatic printing method is characterized in that a printing operation can be performed while a material to be printed is fed continuously at a constant speed, but the actual working of this printing involves various difficulties. For example, in the automatic screen printing machine of this type, since a screen frame is always reciprocated in the horizontal direction, precise location of the screen is often difficult.
When the screen is not precisely located, patterns of respective repeats are made discontinuous or superimposed. Further, when patterns having a plurality of colors are printed, a plurality of screens corresponding to the number of colors to be printed must be used and in this case, matching of the phases among the screens is very important. If there is a deviation of the phases or relative positions among the screens, a so-called color shear is caused in an obtained print. In the screen printing machine of the above-mentioned type where a material to be printed is continuously fed in the printing zone, the phase adjustment is very difficult and the position or phase of the screen is readily deviated by the reciprocative movement of the screen, and it is often difficult to obtain prints having a precisely registered pattern.
In conventional screen printing machines of the type where a screen is driven, for example, rotary screen printing machines, a phase adjustment mechanism is disposed in a screen driving system and the phase of the screen is adjusted by reducing or increasing the screen driving speed by this phase adjustment mechanism. However, in printing machines of the above-mentioned type where a material to be printed is continuously fed, the operation of moving the screen at the same speed as that of the material in the same direction as that of the material at the printing step, the operation of moving the screen in the reverse direction during the non-printing period, the operation of scanning the squeegee member on the screen at the printing step, the operation of contacting the material to be printed with the screen at the start of the printing step and separating the material from the screen at the completion of the printing step and the operation of continuously feeding the material to be printed at such a speed that the material is moved along a distance corresponding to one repeat length while one cycle of the printing operation is completed must be performed at good timings accordantly with one another. Accordingly, in the printing machines of this type, it is quite difficult to perform the phase adjustment by a phase adjustment mechanism disposed in the screen driving system.